Depending on the jurisdiction district attorneys have different responsibilities. A district attorney is according to Wikipedia.org "an elected or appointed governmental official who represents the government in the prosecution of criminal offenses." However in many criminal cases the attorneys responsible for trying cases are assistant district attorneys or deputy district attorneys.
District attorneys exist at the federal state and county levels across the United States. In all federal courts state courts and depending on the size of the county court the district attorney's office normally consists of several licensed attorneys paralegals legal assistants and individuals who assist with case research. All of these employees work together to build cases against alleged criminals.
The district attorney's office is in charge of determining whether or not a criminal case should go to trial. If the office does not believe it has enough evidence to effectively prosecute they will not pursue a trial or attempt a conviction. The job of a district attorney comes with a huge amount of responsibility and pressure – especially when trials receive an abundance of media coverage. Additionally there are usually more cases in the pipeline than the district attorney's office can easily prosecute at any given time. Nonetheless all cases must get handled as required by law.
It takes a law degree and years of experience to be elected or appointed to the position of district attorney and the average yearly salary according to salaryexpert.com is $90000 to $140000.